The X-ray structure of ammonium decavanadate hexahydrate was redetermined at a low temperature (100 K) in order to locate the hydrogen sites and to study the hydrogen bonds. The hydrogen atoms were assigned to the appropriate atomic group, NH4+ cations, and water molecules, missing to the best of our knowledge in the literature. A kappa refinement was performed to estimate the experimental atomic charges. These charges were used to generale the electrostatic potential on the molecular surfaces of decavanadate polyanions isolated from the influence of the crystal lattice. Comparisons with previous theoretical (ab initio) calculations were made and are also discussed